a. Field of the Invention
The invention relates to devices to remove undesirable solids and, generally, to remove a second separate liquid phases from a first liquid phase. More specifically, the invention relates to devices to separate metal cuttings and other solids as well as machine oil from coolant to render the coolant suitable for reuse in machining metal parts. Applications include, but are not limited to, processing of coolants from metalworking, metal finishing, screw machines, grinding/lapping, and primary metals such as roll forming, cold heading and stamping.
b. Description of the Prior Art
Machining metal parts generates friction and, consequently, heat. This heat and friction tend to wear out the cutting implements used to machine metal parts. Therefore, it has long been the practice to use lubricating oils (also known as way lube) to reduce the friction of moving machine parts and to spray coolants on the workpiece to dissipate the heat generated. The coolant sprayed on the workpiece being machined also carries away metal shavings and lubricating oil. Metal shavings carried away by the coolant are known as "swarf," and lubricating oil picked up by the coolant is known as "tramp oil." The oil and coolant form an emulsion, not a mixture. The oil and water remain in separate phases. Upon standing the lighter oil phase tends to rise to the top and the heavier coolant phase tends to settle to the bottom of a vessel. The oil phase covering the coolant creates an anaerobic environment promoting the growth of anaerobic bacteria. Growth of anaerobic bacteria causes the pH of the coolant to drop, i.e., become more acidic. Acidic coolant dissolves, to some extent, metals from the cutting tools and workpieces upon which it is sprayed. This dissolving of cutting tools and workpieces causes wear of the cutting tools and surface degradation of workpieces. In addition, some of the metallic ions dissolved are heavy metals which present health hazards to workers.
Systems for removing swarf and tramp oil from coolant are well known. Systems are commercially available from EdjeTech Services, Inc., Hyde Products, Inc. Total System Partnership and others. U.S. Pat. No. 5,599,457 to Fanning et al. discloses a machine coolant treatment method. The method comprises the following steps: (1) passing the coolant through an oil absorbent filter to produce a first filtrate free of tramp oil; (2) passing the filtrate through a particle filter to producer a second filter to produce a second filtrate substantially free of particulate matter; and (3) passing the second filtrate through at least one porous metal sponge-like structure formed of metal particles bound together in an interconnected form to produce a coolant free of tramp oil, particulate matter and dissolved heavy metals. The pH and bacterial growth are controlled by passage of the coolant through the porous metal sponge-like structure. The problem with Fanning's invention is that the oil absorbent filter and particle filter have to be regularly cleaned or the oil-removing efficiency will be diminished. The oil is removed in the oil absorbent filter, and this oil absorbent filter has a maximum carrying capacity.
U.S. Pat. No. 5,244,586 to Hawkins et al. discloses a machine coolant recycling system. Hawkins teaches the use of a centrifuge to separate the undesirable oil and solids from the coolant. Hawkins, like many of the prior art systems is too complicated to be dedicated to a particular machine within a metal-working shop. Instead, as noted in Hawkins, coolant from each machine's sump was transferred to a central recycling system which typically served a large number of metal-working machines. Hawkins invention is too complicated and bulky to be used for a single metal-working machine, so it would not be practical where a machine shop only had a few metal-working machines or where a central recycling system was for some reason impractical.